Bad service and incorrect billing

Good day All

It appears Im having another issue with this account again,my story goes as follows, recently I upgraded my phone and seems to have been downhill from there, initially I was given a Sim card that was faulty and it took over a month to rectify then a few weeks later I received an sms saying my account had been changed from debit order to cash. The funny thing is that I haven't been a debit order customer since we had our last incident, so I called the customer car line and spoke to a Roshnee who was very helpful even though I was irritated by it all, she told me that the agent, 'Siza' who handled my upgrade at the Westgate store put my account as a debit order and mtn kept billing me for returned debits, never mind that its an account that I also close years ago I don't even remember it. So yesterday I called her and she told me a story about paying in arrears Bla Bla which I ddnt understand because I have never skipped any payments, iv only paid late due to some issues with my account but I still paid the full amount plus the penalty which was around 700 odd Rands. So I don't understand why mtn sends me a text saying I owe r600 because of returned debits etc...to top it off they don't even have my correct details on from passport number to bank account so who is to blame here? .. Is it not enough headache now to just maybe give up and seek refuge with another service provider who is more proactive and organised than this? I'm. Really fed up with this Mtn story and very close to just closing the account.